Rapidly propelled gas is used in ion thrusters to accelerate space vehicles and in systems for implanting ions in semiconductors and other materials. To accelerate the gas, it is generally first brought from a source at ground potential to a high potential where acceleration of the gas occurs. As the gas moves between ground and a high potential, ionization occurs which can lead to uncontrolled current conduction through the gas. Such current flow is minimized by providing an isolator between the two widely different potentials, the isolator typically forming a long tube of insulative or dielectric material. U.S. Pat. No. 3,576,107 describes an isolator formed by deep interfitting cylinders that have deep concentric grooves. The formation of such deep concentric grooves is difficult, and results in wide passages. It is desirable to form the passages with a large surface area per unit length, to maximize recombination of ions and electrons so as to minimize the conductivity of the gas. A gas isolator which was of simple and compact construction, and which provided a very long and narrow passage through which gas passes between locations of widely different potential, would be of considerable value.